One known design of aerator/mixer in use at present consists of a rotatable hollow drive shaft with air intake ports at one end, open at the other end, and a propeller adjacent said other end. In use, the aerator/mixer is mounted with the propeller immersed in the wastewater or other liquid to be aerated/mixed, but with the air intake ports above the water line.
The drive shaft is rotated (e.g. by an electric motor) to drive the propeller. The rotation of the propeller mixes the liquid in which the propeller is immersed, and also induces a fluid flow across the lower, immersed, end of the drive shaft. This creates an area of reduced pressure at the lower end of the drive shaft, and hence a similar reduction of pressure at the air intake ports, drawing atmospheric air into the ports and down the shaft.
The air so drawn into the shaft is released as small air bubbles into the liquid flow pattern created by the propeller.
In wastewater treatment processes, aeration introduces air into a liquid, providing an aerobic environment for microbial degradation of organic matter. The purpose of aeration is two-fold:
1. To supply the required oxygen for metabolizing micro-organisms.
2. To provide mixing so micro-organisms come into intimate contact with the dissolved and suspended organic matter.